The OEIS is supported by the many generous donors to the OEIS Foundation.

 Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 59th year, we have over 358,000 sequences, and we’ve crossed 10,300 citations (which often say “discovered thanks to the OEIS”). Other ways to Give
 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A308449 Numbers k such that 25*10^(2*k) + 5*10^k + 1 are prime. 1
 0, 1, 2, 14, 174, 448 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 LINKS EXAMPLE 31 is prime ==> a(1) = 0. 2551 is prime ==> a(2) = 1. 250501 is prime ==> a(3) = 2. 25005001 = 7 * 79 * 103 * 439. 2500050001 = 19 * 2269 * 57991. 250000500001 = 7 * 103561 * 344863. PROG (PARI) for(k=0, 1e3, if(ispseudoprime(25*100^k+5*10^k+1), print1(k", "))) CROSSREFS Cf. A309738. Sequence in context: A235369 A351274 A228476 * A233224 A167014 A300282 Adjacent sequences: A308446 A308447 A308448 * A308450 A308451 A308452 KEYWORD nonn,more,base AUTHOR Seiichi Manyama, Aug 15 2019 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified December 6 05:22 EST 2022. Contains 358594 sequences. (Running on oeis4.)